Equipartition Theorem (Thermal Physics)

I just wanted to know whether the following formula 3/2kT=K (ave) demonstrates the average kinetic energy per atom in a monatomic gas.
And then if 5/2kT=K (ave) demonstrates the average kinetic energy per diatomic molecule.

This comes from the fact that the average energy per degree of freedom is 1/2kT.

Yes, you are correct. The equipartition theorem breaks down at low temperatures when the energy kT is smaller than the energy spacing in a degree of freedom. It doesn't have enough energy to make that jump, so that degree of freedom becomes frozen out.